1. Field of the Invention
The present invention relates to a film forming supplying process solution to a substrate that is rotated so as to spread out the process solution on the substrate and form a film of the process solution on the substrate.
2. Description of the Related Art
In the art of semiconductor fabrication, when a semiconductor layer, an insulation layer, and an electrode layer on an LCD (Liquid Crystal Display) substrate are selectively patterned and etched, as with the case of a semiconductor wafer, a resist film is formed on the front surface of the LCD substrate. To form such a resist film, a spin coater has been used.
The spin coater has a spin chuck, a rotation cup, and a driving motor. The spin chuck rotates an LCD substrate thereon. The rotation cup surrounds all the periphery of the spin chuck. The driving motor rotates the spin chuck and the rotation cup. When a resist film is formed on an LCD substrate by the spin coater, resist solution is dropped at the center portion of the LCD substrate that is rotated. Thus, the resist solution is concentrically spread out by centrifugal force.
Although the resist solution dropped on the LCD substrate starts concentrically spreading out, the resist solution may not equally reach the periphery of the LCD substrate. In this case, the resist solution may break on the LCD substrate. Thus, the resist film may not be equally formed on the LCD substrate. To solve this problem, the resist solution is excessively dropped to the LCD substrate. Thus, the resist solution is fully formed on the entire front surface of the LCD substrate. In this method, however, it is impossible to reduce the quantity of the resist solution. In addition, when the rotating acceleration of the LCD substrate is low, the resist solution that concentrically spreads out breaks on the LCD substrate. Thus, the resist solution cannot be fully formed on the front surface of the LCD substrate.
To solve such a problem, conventionally, a high torque motor was sometimes used. In other words, by rotating the LCD substrate with a high torque motor, centrifugal force applied to the resist solution is strengthened. Thus, the resist solution equally and concentrically spreads out from the center of the LCD substrate to the periphery thereof. Consequently, the quantity of the resist solution can be reduced. In addition, the resist film with an equal thickness can be formed on the front surface of the LCD substrate.
However, since the sizes of LCD substrates are becoming large, they are becoming heavy. Thus, it is difficult to rotate an LCD substrate at a large rotating acceleration. In addition, a high torque motor that can rotates an LCD substrate at a large rotating acceleration is currently not available. Even if such to a motor becomes available, the apparatus becomes large and expensive. In addition, the footprint becomes large. Moreover, until the LCD substrate rotates at a predetermined rotating speed, it takes a long time. Thus, the resist solution may not equally spread out from the center of the LCD substrate to the periphery thereof. Consequently, unless the resist solution is excessively dropped, the resist film with the equal thickness cannot be formed.
The present invention is made from the above-described point of view. An object of the present invention is to provide a film forming apparatus and a film forming method that allow the quantity of process solution supplied to a substrate to be decreased and a film of the process solution to be formed on a process surface of the substrate at low cost.
An aspect of the present invention is a film forming apparatus for supplying process solution to a substrate, spreading out the process solution on the substrate, and forming a film of the process solution on the substrate, comprising a driving means for rotating the substrate, wherein said driving means has a main driving mechanism, an auxiliary driving mechanism for assisting the driving of said main driving mechanism, and a controlling means for causing the operation time of said assisting driving mechanism to overlap with the operation time of said main driving mechanism.
According to the present invention, the operation time of the main driving mechanism and the operation time of the auxiliary driving mechanism that assists the driving of the main driving mechanism can be temporarily overlapped. Thus, even if the size of a substrate becomes large, it can be rotated at a large rotating acceleration. Consequently, the process solution supplied to the substrate can be equally and concentrically spread out to the periphery of the substrate. As a result, the film of the process solution can be formed on the substrate with an equal thickness.
These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawings.